More about grades of fertilizers for those who are interested:
Nutrient Types
When looking at the huge range of hydroponic liquid nutrient concentrates in your local store you will essentially find two main types: single part (pack) concentrates and two or more part (or multi part) concentrates.
Lets first look at a multi part (pack) concentrate. Why do they put it into two different packs? The answer to this is very simple: to avoid the precipitation or lock out that occurs when certain mineral elements are placed together in concentrate. The elements separated are the phosphates and sulfates from the calcium source. This is done because calcium reacts with those elements, forming new compounds, i.e. gypsum salts. These new compounds are typically seen as a white precipitate or sludge in the bottom of the bottle (look at most one parts and you will see this).
Multi-part nutrients also offer the advantage of flexibility. When using a multi-part concentrate you can alter the ratios to suit certain conditions. For instance, you could add a little more nitrogen and calcium or extra micronutrients if the conditions warrant it. So you have flexibility as well as a non-precipitated solution to give to your plants.
Single parts, on the other hand, place all the elements together in one bottle. The trade off for this convenience can be lack of full availability of elements and lack of flexibility.
Available now are one-part concentrates that have no precipitation. These are a much better choice, as all the elements contained within the bottle are available to your plants. A very easy way to test whether you have a good one-part nutrient is to shake the bottle vigorously and then decant some into a glass or clear container. After an hour or so, carefully and very slowly pour the solution back into the bottle. If you notice any significant precipitate or sludge on the bottom, then nutrient reaction or lock out has occurred. It is important to know this because when these elements combine and precipitate, they are almost always permanently unavailable to the plant.
If you look at the label on a bottle of nutrients you will see some brands with chelated micronutrients and others without. But what are chelates? And how do they work? A quick reference to the original Greek meaning (claw-like) gives us an accurate explanation. Chelates are molecules that hold (with their claws) other elements within them. Another way of looking at chelates is as a cage with the micronutrient held inside the cage. In respect to plants, chelates function at a number of different levels. Firstly, they protect the element (inside the claw or cage) from undesirable solution, and secondly, they make elements more available to the plant by acting as transporters.
To explore the protection concept further, lets look at micronutrients that are commonly chelated in nutrient concentrates. Micronutrients, especially Copper, Manganese, Zinc and Iron, are particularly susceptible to unfavorable conditions (i.e. pH shifts, UV light etc). Under these conditions they will become unavailable to the plants, or fall out of solution, making them unavailable for absorption (because they arent there!). By protecting our micronutrients with chelates, we make them significantly more available to the plants over a wider range of conditions.
As for the chelates role in element transportation, think of them as little microscopic four-wheel-drive trucks carrying a load of goods to the plant. These trucks can pass through any condition or difficult terrain in order to distribute their goods. In other words, chelates carry the elements through the root membrane even when prevailing root conditions would make absorption or transportation quite limited. So chelates are very important to the hydroponic gardener. They make life a lot easier for the plants and for us (no headaches!).
Now that we know a little more about chelates and micronutrients we come to the very important, but often overlooked, issue of element or formulation purity. So what is chemical element purity, and how can a consumer ensure this purity? To help explain this, lets examine what makes a chemical pure or impure. We can then look briefly at a couple of different chemical grades or standardized chemical purity levels.
The most important factor that makes a chemical or element pure or impure is the relative amount of that element (or elements, in a compound) compared to other elements that are not required. For example, if a chemical, lets say Phosphorus, is said to be 99.5% pure, this means it contains 99.5% of the required element (phosphorus in this case). The same would be true for a compound like Potassium Nitrate (which contains both calcium and nitrogen). It would contain 99.5% of the multiple elements. The remaining 0.5% would be made up of other elements that are present but not required (i.e. impurities).
It is these other non-essential elements that often pose problems for the hydroponic grower because many are toxic to plants, even in minute quantities. Some common impurities found in many chemicals are Lead, Mercury, Cadmium, Arsenic and Perchlorates. Perchlorates are extremely detrimental to the growth of particular plant species, even in the smallest amount. The other elements listed are all heavy metals. They slow the metabolic processes of the plants, thereby slowing the growth of the plant and hence the yield, which is definitely a very bad thing! This being said, it should be remembered that not all impurities have direct detrimental effects on plants.
As a consumer, the purity question can be overwhelming. Fortunately there are four types of chemical grades (standards) that put this information into perspective. These grades outline the types of chemicals many manufacturers of nutrients use, while clarifying the relative purity of these chemicals.
The four types of chemical grades we need to look at in hydroponics are Fertilizer or Industrial Grade, Technical Grade, British Pharmaceutical Grade and Laboratory Reagent Grade.
Fertilizer or Industrial grade is the lowest (worst). This grade is typically less than 90% pure and contains the largest amount of impurities.
Technical grade is better. It is typically around 90% to 95% pure, but it can still contain quite a lot of impurities, including detrimental elements.
British Pharmaceutical grade is the most preferable grade of material. It is approximately 99% pure, and it is tested to be free of any heavy metals and perchlorates. The standards for this grade are more stringent because these products are typically used in the manufacturing of foodstuffs and pharmaceuticals (which explains why the common slang name for British Pharmaceutical Grade is Food Grade).
Laboratory Reagent Grade is above 99.5% purity, but sometimes it does not undergo specific heavy metal and perchlorate testing.
Many manufacturers make their nutrient concentrates from fertilizer and technical grades because they are significantly cheaper (around one-quarter the price).
Ive been using it the last year and love it. But it still doesn't have much info on it.
